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Making your own Coqui

Ingredients

(pick one or several) -- a photoresistor; a potentiometer; a thermistor

Here's a digikey shopping cart with enough of the above ingredients (+ extras) for Coqui kits, at a cost of $19 per kit + shipping.

Schematic

The basic circuit for Coqui BBv1.0 is this:

The frequency of the output is a function both of the resistance, 'R' (which can be either a resistor, or some water between two electrodes, or a photoresistor, or a thermistor, or a potentiometer ... anything that will provide an electrical connection, with some resistance), and a capacitor, 'C'.

The frequency of output is given by: 0.7/(R*C).

Note -- the 555 chip is oriented in this picture such that the little 'circle' or 'divot' in the chip is oriented downwards. E.g., this chip (which has both a 'circle' and a 'divot') share the same orientation in this photo:

And this is what it looks like on the breadboard:

Quick notes:

the green 'R' in the diagram is a resistor that tunes the frequency of the 555 output (which we'll be hearing via a speaker)

the blue 'C' in the diagram is a capacitor. For low conductivity solutions, 0.1 uF is a good range to use. For higher conductivity solutions (like salt water), 1.0 uF, or even 10.0 uF, might be better values to use, in order to keep the output frequency in the audible range.

Since the two main ways to control the sound are the saltiness of the water and the size of the capacitor, it would be cool if this list of parts included some other sizes of capacitors in addition to the 10uF, like a 1 and a 2.2.

Other supplies needed to do the things shown in the video demos include: